Speed control for hydraulic transmission

ABSTRACT

A speed control for a hydraulic transmission having a pump and motor in series has a pair of pumps in an auxiliary series circuit, one of the pair being driven by the motor shaft and the other of the pair being driven at a known reference speed. A pressure difference across the pair of pumps is used to position an actuator which controls the stroke of the motor.

United States Patent Morris 51 Sept. 26, 1972 [54] SPEED CONTROL FORHYDRAULIC TRANSMISSION [72] Inventor: John Morris, The Gable, Plex MossLane, Halsall, near Ormskirk, England [22] Filed: Dec. 11, 1970 [21]Appl. No.: 97,222

[52] US. Cl. ..60/52 VS, 60/53 R [51] Int. Cl. ..Fl5b 15/18, F16d 31/06[58] Field of Search ..60/53 R, 52 VS [56] References Cited UNITEDSTATES PATENTS 2,983,101 5/1961 Tyler ..60/53 R Kempson et a1. "60/53 RTyler ..60/52 VS Primary Examiner-Edgar W. Geoghegan AssistantExaminerA. M. Zupcic AttorneyHo1man & Stern 5 7 1 ABSTRACT A speedcontrol for a hydraulic transmission having a pump and motor in serieshas a pair of pumps in an auxiliary series circuit, one of the pairbeing driven by the motor shaft and the other of the pair being drivenat a known reference speed. A pressure difference across the pair ofpumps is used to position an actuator which controls the stroke of themotor.

5 Claims, 1 Drawing Figure PATENTED was I972 NVENTOR f ATTORNEYS SPEEDCONTROL FOR HYDRAULIC TRANSMISSION This invention relates to speedcontrol apparatus for hydraulic power transmission systems which includeone or more pumps and one or more motors driven therefrom and in whichthe speed of the motor or motors is controlled by regulating the outputflow of the pump or pumps.

A speed control apparatus of the type specified comprises a first pumphydraulically coupled to a motor whose speed is to be controlled, asecond and third pump hydraulically coupled in a closed loop, the saidsecond pump being mechanically coupled to said motor, independent meansfor driving said third pump, means for setting the output of said thirdpump to a desired value, and actuating means responsive to a pressuredifference across said second and third pumps and adapted to alter, inuse, the output of the first pump.

Reference will now be made to the accompanying drawing which showsdiagrammatically and by way of example a control apparatus according tothe invennon.

A first pump having its stroke variable by an actuator in the form of adouble-acting piston and cylinder unit 22 and driven by a shaft 11drives via pressure and return lines l2, 13 respectively, a motor 14having a fixed stroke and connected to an output shaft 15. A second pump16 having a fixed stroke has its shaft mechanically coupled to the shaftof the motor 14. A third pump 17 having a stroke variable by a controlmeans 18 is hydraulically coupled in a closed loop to the second pump 16by lines 19, 20, the direction of flow in the example being from thepump 17 via line 19 to pump 16 and thence via line 20 back to pump 17.The pump 17 is driven by a shaft 21.

The actuator 22 is hydraulically connected across the pumps 16, 17 andco-acts with the pump 10 so that, in use, it increases or decreases theoutput flow of the pump 10 when the pressure is the greater in line 19or line 20 respectively. Non-return valves 23, 24 connect lines 19, 20respectively to the line 13. A line 25 with an associated needle valve26 permits a proportion of the flow in the closed loop to pass throughthe line 25 when the pressure difference between lines 19 and 20 issufficient to operate the valve 26. Pumps 10, i6, 17 and motor 14include drains which are connected to a low pressure return line 27.

In use the pump 10 is driven at a substantially constant speed by theshaft 11, and in turn drives the motor 14 at a speed proportional to theoutput flow of the pump 10. The pump 17 is driven, also at asubstantially constant speed by the shaft 21.

Assuming initially that the outputs of the pumps 16, 17 are equal, thepressures in the lines 19, 20 will be equal and the actuator 22 will notbe urged to vary the output of the pump 10. [f the output of the pump 17is increased by operation of the control means 18, the resultantincreased pressure in the line 19 operates the actuator 22 so as toincrease the output flow of the pump 10 and thereby to increase thespeed of the motor 14 until the consequent increase in the output of thepump 16 causes the pressures in the line 19, 20 once more to be equal.Reduction of the output of the pump 17 will act in a like manner toreduce the speed wit 'iii oiiibut of the pump 17 at a constant value theapparatus will operate as previously described to tend to vary theoutput of the pump 10 so as to overcome any variation in the speed ofthe motor 14.

Having thus described my invention what 1 claim as new and desire tosecure by Letter Patent is:

l. A speed control apparatus for a hydraulic power transmission systemhaving a pump and a motor driven therefrom and in which motor speed iscontrolled by regulating the output of the pump comprises a first pumphydraulically coupled to a motor whose speed is to be controlled, atsecond and third pump hydraulically coupled to a closed loop, the saidsecond pump being mechanically coupled to said motor, independent meansfor driving said third pump, means for setting the output of said thirdpump to a desired value, and actuating means responsive to a pressuredifference across said second and third pumps and adapted to alter, inuse, the output of the first pump.

2. An apparatus as claimed in claim 1 which includes a pressureresponsive valve in parallel with the second and third pumps, the saidvalve bypassing a proportion of the flow in the said loop when the saidpressure difference exceeds a predetermined value.

3. An apparatus as claimed in claim 1 in which the actuating means isresponsive to an increase in pressure downstream of the second pump toreduce the output of the first pump and to a decrease in the saiddownstream pressure to increase the output of the first pump.

4. An apparatus as claimed in claim 1 which includes a pair ofnon-return valves by means of which the upstream and downstream sides ofthe second pump respectively communicate with the downstream side of themotor.

5. An apparatus as claimed in claim 1 in which the actuating meanscomprises a double'acting piston and cylinder unit.

i l i i UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3,693,349 Page 1 of 2 APPLICATION NO. 05/097222DATED September 26, 1972 INVENTOR(S) Morris It is certified that errorappears in the above-identified patent and that said Letters Patent ishereby corrected as shown below:

Delete Drawing Sheet 1 and Substitute therefor the Drawing Sheetconsisting of FIG 1 as shown on the attached page.

Signed and Sealed this Sixteenth Day of December, 2008 ,rrga

JON W. DUDAS Director afthe United States Patent and Trademark OflicePage 2 of2 Sep. 26, 1972 U.S. Patent

1. A speed control apparatus for a hydraulic power transmission system having a pump and a motor driven therefrom and in which motor speed is controlled by regulating the output of the pump comprises a first pump hydraulically coupled to a motor whose speed is to be controlled, a second and third pump hydraulically coupled to a closed loop, the said second pump being mechanically coupled to said motor, independent means for driving said third pump, means for setting the output of said third pump to a desired value, and actuating means responsive to a pressure difference across said second and third pumps and adapted to alter, in use, the output of the first pump.
 2. An apparatus as claimed in claim 1 which includes a pressure responsive valve in parallel with the second and third pumps, the said valve bypassing a proportion of the flow in the said loop when the said pressure difference exceeds a predetermined value.
 3. An apparatus as claimed in claim 1 in which the actuating means is responsive to an increase in pressure downstream of the second pump to reduce the output of the first pump and to a decrease in the said downstream pressure to increase the output of the first pump.
 4. An apparatus as claimed in claim 1 which includes a pair of non-return valves by means of which the upstream and downstream sides of the second pump respectively communicate with the downstream side of the motor.
 5. An apparatus as claimed in claim 1 in which the actuating means comprises a double-acting piston and cylinder unit. 